Bioactivity of Polyphenols: Preventive and Adjuvant Strategies toward Reducing Inflammatory Bowel Diseases—Promises, Perspectives, and Pitfalls

Table 1

Overview of major risk factors and suggested mechanisms involved in the development of IBD.

Risk factor	Influence: positive (+), negative (−)	Mechanism	Reference
Genetic predisposition	+/−	Genes involved in inflammation and oxidative stress responses and in immune function (histocompatibility complex)	[19, 33]
Smoking	−	Altered blood flow, enhanced cytokine formation, immunomodulatory, influencing mucus production	[18]
Air pollution (NOx, SO2…)	−	Unclear: proinflammatory response to air particles?	[18]
Enhanced hygiene	−	Unclear: reduced exposure early in life to microorganisms. Reduced IBD prevalence found for growing up on farms, living in crowded homes, consuming unpasteurized milk	[18]
Microbiota	+/−	Immunomodulatory properties, production of anti-inflammatory compounds. Some bacteria strains associated with negative effects (e.g., Clostridia), others with positive effects, such as Bifidobacteria, possibly due to enhanced gut barrier properties, production of SCFA	[34]
Diet, probiotics	+	Immunomodulatory properties, production of anti-inflammatory compounds, see microbiota	[28]
Diet, prebiotics (fiber)	+	Favouring healthy microbiota (Bifidobacteria…), production of anti-inflammatory SCFA, lowering of pH	[28]
Diet, vitamin D	+	Immunomodulatory, protection of barrier	[35]
Diet, dietary fiber	+	Production of anti-inflammatory SCFA, increasing fecal bulk and lowering concentration of compounds with adverse effects	[17, 26]
Diet, vitamins C, E	+/−	Unclear: antioxidants may reduce ROS parameters, normalize abnormally low tissue levels in subjects with IBD	[36]
Diet, PUFAs (-3)	+	Anti-inflammatory effects	[37]
Diet, polyphenols	+	Antioxidant effects (reducing ROS), anti-inflammatory properties, altering genetic expression via NF-B, Nrf-2, improving barrier properties, immunomodulatory	[13, 38–40]

PUFAs: polyunsaturated fatty acids, ROS: reactive oxygen species, and SCFA: short-chain fatty acids.